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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35bbaf9452asm1653656a91.12.2026.03.19.01.56.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Mar 2026 01:56:39 -0700 (PDT) Message-ID: <4d6f78d3-f274-43e1-adc8-c4fff4f85e24@suse.com> Date: Thu, 19 Mar 2026 19:26:34 +1030 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] btrfs: Fix BTRFS arm64 tagged KASAN false-positive To: Daniel J Blueman , Chris Mason , David Sterba Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260319053413.14771-1-daniel@quora.org> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXVgBQkQ/lqxAAoJEMI9kfOh Jf6o+jIH/2KhFmyOw4XWAYbnnijuYqb/obGae8HhcJO2KIGcxbsinK+KQFTSZnkFxnbsQ+VY fvtWBHGt8WfHcNmfjdejmy9si2jyy8smQV2jiB60a8iqQXGmsrkuR+AM2V360oEbMF3gVvim 2VSX2IiW9KERuhifjseNV1HLk0SHw5NnXiWh1THTqtvFFY+CwnLN2GqiMaSLF6gATW05/sEd V17MdI1z4+WSk7D57FlLjp50F3ow2WJtXwG8yG8d6S40dytZpH9iFuk12Sbg7lrtQxPPOIEU rpmZLfCNJJoZj603613w/M8EiZw6MohzikTWcFc55RLYJPBWQ+9puZtx1DopW2jOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXWBBQkQ/lrSAAoJEMI9kfOhJf6o cakH+QHwDszsoYvmrNq36MFGgvAHRjdlrHRBa4A1V1kzd4kOUokongcrOOgHY9yfglcvZqlJ qfa4l+1oxs1BvCi29psteQTtw+memmcGruKi+YHD7793zNCMtAtYidDmQ2pWaLfqSaryjlzR /3tBWMyvIeWZKURnZbBzWRREB7iWxEbZ014B3gICqZPDRwwitHpH8Om3eZr7ygZck6bBa4MU o1XgbZcspyCGqu1xF/bMAY2iCDcq6ULKQceuKkbeQ8qxvt9hVxJC2W3lHq8dlK1pkHPDg9wO JoAXek8MF37R8gpLoGWl41FIUb3hFiu3zhDDvslYM4BmzI18QgQTQnotJH8= In-Reply-To: <20260319053413.14771-1-daniel@quora.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/3/19 16:04, Daniel J Blueman 写道: > When booting Linux 7.0-rc4 on a Qualcomm Snapdragon X1 with KASAN > software tagging with a BTRFS filesystem, we see: > > BUG: KASAN: invalid-access in xxh64_update (lib/xxhash.c:143 lib/xxhash.c:283) > Read of size 8 at addr 7bff000804fe1000 by task kworker/u49:2/138 > Pointer tag: [7b], memory tag: [b2] > > CPU: 0 UID: 0 PID: 138 Comm: kworker/u49:2 Not tainted 7.0.0-rc4+ #34 PREEMPTLAZY > Hardware name: LENOVO 83ED/LNVNB161216, BIOS NHCN60WW 09/11/2025 > Workqueue: btrfs-endio-meta simple_end_io_work > Call trace: > show_stack (arch/arm64/kernel/stacktrace.c:501) (C) > dump_stack_lvl (lib/dump_stack.c:122) > print_report (mm/kasan/report.c:379 mm/kasan/report.c:482) > kasan_report (mm/kasan/report.c:597) > kasan_check_range (mm/kasan/sw_tags.c:86 (discriminator 1)) > __hwasan_loadN_noabort (mm/kasan/sw_tags.c:158) > xxh64_update (lib/xxhash.c:143 lib/xxhash.c:283) > btrfs_csum_update (fs/btrfs/fs.c:106) > csum_tree_block (fs/btrfs/disk-io.c:103 (discriminator 3)) > btrfs_validate_extent_buffer (fs/btrfs/disk-io.c:389) > end_bbio_meta_read (fs/btrfs/extent_io.c:3853 (discriminator 1)) > btrfs_bio_end_io (fs/btrfs/bio.c:152) > simple_end_io_work (fs/btrfs/bio.c:388) > process_one_work (./arch/arm64/include/asm/jump_label.h:36 ./include/trace/events/workqueue.h:110 kernel/workqueue.c:3281) > worker_thread (kernel/workqueue.c:3353 (discriminator 2) kernel/workqueue.c:3440 (discriminator 2)) > kthread (kernel/kthread.c:436) > ret_from_fork (arch/arm64/kernel/entry.S:861) > > The buggy address belongs to the physical page: > page: refcount:3 mapcount:0 mapping:f1ff00080055dee8 index:0x2467bd pfn:0x884fe1 > memcg:51ff000800e68ec0 aops:btree_aops ino:1 > flags: 0x9340000000004000(private|zone=2|kasantag=0x4d) > raw: 9340000000004000 0000000000000000 dead000000000122 f1ff00080055dee8 > raw: 00000000002467bd 43ff00081d0cc6f0 00000003ffffffff 51ff000800e68ec0 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff000804fe0e00: 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b > ffff000804fe0f00: 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b >> ffff000804fe1000: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 > ^ > ffff000804fe1100: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 > ffff000804fe1200: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 > > This occurs as contiguous pages may have different KASAN tags in the upper address > bits, leading to a tag mismatch if linear addressing is used. > > Fix this by treating them as discontiguous. > > Signed-off-by: Daniel J Blueman > Fixes: 397239ed6a6c ("btrfs: allow extent buffer helpers to skip cross-page handling") > > --- > fs/btrfs/extent_io.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 5f97a3d2a8d7..e2b241fb6c0e 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -3517,8 +3517,16 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, > * At this stage, either we allocated a large folio, thus @i > * would only be 0, or we fall back to per-page allocation. > */ > - if (i && folio_page(eb->folios[i - 1], 0) + 1 != folio_page(folio, 0)) > - page_contig = false; > + if (i > 0) { > + struct page *prev = folio_page(eb->folios[i - 1], 0); > + struct page *curr = folio_page(folio, 0); > + > + /* > + * Contiguous pages may have different tags; can't be treated as contiguous > + */ > + if (curr != prev + 1 || page_kasan_tag(curr) != page_kasan_tag(prev)) > + page_contig = false; I am not a fan of this solution. Although it doesn't affect end users who don't have KASAN soft tag enabled, I don't get what we can really get from the different tags. I mean all those pages are already contig in physical addresses, why we can not access the range in one go? Maybe it will be better to set all pages with the same random tag if page_contig is true? Thanks, Qu > + } > > if (!btrfs_meta_folio_test_uptodate(folio, eb)) > uptodate = 0;